In fabrication of semiconductors, the minimum line width of the circuit element is called critical dimension (CD). The smaller the circuit element is, the less variation of the CD is allowed. Thus, many techniques for improving the critical dimension uniformity (CDU) are developed, and exposure-dose control system, which is named DoseMapper (DOMA) and developed by ASML Company, is a typical one of such techniques.
However, CDU improvement is just one of the factors should be considered during fabrication of semiconductors. There is also a desire to improve uniformity of electrical characteristics of different devices at different positions of a wafer.